VII. Adjusting Muscle Tension

A.Muscles as a whole can have graded contractions for tasks 1. A twitch contraction is a brief contraction of all fibers in response to a single action potential 2. Record of a contraction is a myogram a. Has latent, contraction and refractory sections b. Refractory period is the time the muscle has lost excitability 1. Short in skeletal long in cardiac

B. Wave (temporal) summation 1. It is the increased strength of contraction resulting from the application of a second stimulus before the muscle has completely relaxed after a previous stimulus 2. A sustained contraction that permits partial relaxation between stimuli is called incomplete(unfused) tetanus

3. complete (fused) tetanus does not even allow the partial relaxation 4. In treppe (staircase effect), each of the first few contraction is stronger than the last

C. Tension 1. A fiber has its greatest tension when there is optimal overlap of thick and thin filaments 2. Increasing the number of active motor units is called recruitment a. Prevents fatigue and stops jerky movements

3. Active and passive tension a. Active tension is created by contractile elements; thick and thin filaments b. Passive tension is created by elastic elements; not related to contractions 4. Isotonic movement is a constant load is moved through a range of motion 5. Isometric movement is no muscle shortening but tension is increased

6. Atrophy is the wasting away because of disuse or no nerve supply 7. Hypertrophy is increasing in fiber diameter from forceful, repetitive activity